李萍萍；

Résumé partiel Populus euphratica Oliv.,commonly known as a desert poplar,is a pioneer trees pecies with the charaters of stress resistance and heteromorphic leaves in western China.Previous studies have demonstrated that the structural characteristics of P.euphratica from lanceolate leaves to dentate broad-ovate leaves are related to its eco-adaptability.In the present study,to elucidate the regulation mechanisms of stress tolerance,we focused on the antioxidant capacity of three heteromorphic leaves of P.euphratica.Here the chlorophyll content,the stability of cell membrane,osmotic regulator substance contents and antioxidant system indeices in lanceolate leaves,ovate leaves and dentate broad-ovate leaves,three typical morphological leaves of adult P.euphratica,were studied in different seasons.The results were as follows:1.There were differences in chlorophyll content and chlorophyll a/b among the three morphological leaves.With the change seasons,the content of chlorophyll increased in lanceolate leaves,firstly increased and then decreased in ovate leaves,while it decreased in dentate broad-ovate leaves.The content of chlorophyll a was higher than chlorophyll b in three morphological leaves.And the chlorophyll a/b value in dentate broad-ovate leaves was the highest,follewd by ovate leaves,was the lowest in lanceolate leaves.The chlorophyll contents in ovate leaves and dentate broad-ovate leaves were significantly higher than that of lanceolate leaves in May and July.Although the chlorophyll content in dentate broad-ovate leaves decreased in September,but it increased the utilization of light energy by increasing the chlorophyll a/b value,which was an adaptation to the strong light in summer and shortened light time in autumn in the upper part of the canopy.2.There were differences in the osmotic regulation ability among three types of leaves.With the change of seasons,the contents of proline and soluble protein in heteromorphic leaves of P.euphratica were increased,and the content of soluble sugar decreased in lanceolate leaves,while it decreased firstly and then increased in both ovate leaves and dentate broad-ovate leaves.In general,From lanceolate leaves to dentate broad-ovate leaves,there was an obvious increase in the content of osmotic adjustment substances,indicating that dentate broad-ovate leaves had the strongest osmotic adjustment ability and had strong adaptability to strong light and water deficit stress.3.There were differences in ROS metabolism among three morphological leaves.The rate of the O2·-production firstly increased and then decreased in lanceolate leaves,while it progressively increased both in ovate leaves and dentate broad-ovate leaves.The content of MDA increased in lanceolate leaves,firstly decreased and then increased in ovate leaves,while it decreased in dentate broad-ovate leaves all the time.The relative conductivity values of three morphological leaves changed slightly and the difference was not significant.And Scavenging rate of DPPH firstly decreased and then increased in lanceolate leaves and ovate leaves,while it decreased in dentate broad-ovate leaves.It is noteworthy that compared to the other types of leaves,O2·-production rate was the lowest while MDA content was the highest in lanceolate leaves in September.